With budding breasts and pubic hair, girls are developing earlier than ever. What's causing it? And what are the psychological effects?

Marissa Carter, a Galveston, Texas, housewife, could not believe it when her daughter Sharon, at the tender age of 4, seemed to be developing breasts. The tiny buds that appeared on the little girl's chest were gone within a couple of weeks, but three years later, they reappeared, and this time they grew--along with pubic hair and hair in Sharon's armpits. "I felt this was too early for her to be developing," recalls Carter. "Gosh, I was flat as a board at her age."

So after a series of medical consultations, the Carters (all these names have been changed at the...